As bright pigments such as pearlescent pigments, there have been conventionally known mica flakes, synthetic mica flakes, silica flakes, alumina flakes, glass flakes, graphite flakes, and iron oxide particles composed mainly of alpha-iron oxide crystals, which are coated with metal oxides such as titanium dioxide and iron oxide, and the like. Since such a pearlescent pigment reflects incident light from the outside upon its surfaces and shines brilliantly, it gives a distinctive appearance that has an excellent decorative effect and is rich in variety, when contained in a paint, to the coated surface, or when contained in an ink, to the line or the printed surface, or when contained in a resin composition, to the surface of the resin molding, in synergy with the color tones of the substrates.
For the purpose of improving the decorative effect, the pearlescent pigments are widely used for various use such as automotives, motorcycles, OA equipments, cellular phones, home appliances, various printing matters and writing instruments.
A bright coating composition is reported in which the particle size of a bright pigment is adjusted so as to obtain brightness and prevent a filter from clogging during circulation for coating (see e.g. JP 2002-155240 A).
However, the conventional flaky particles to be applied to the bright pigments for use in an automotive body coating composed of a metallic base layer are made of a material having a refractive index of 1.4 to 1.8, and have an average thickness in the range of 0.3 to 0.7 μm. In the case that the flaky particles have a refractive index and average thickness in such a range, if each particle has a different thickness, the color development of interference light is different in each particle. For this reason, the automotive body coatings to be obtained using these conventional bright pigments have an appearance of a mixture of various colors being present in particles, and thus suffer from lack of color uniformity and color clarity, resulting in a poor design.
Further, as flaky particles to be used for the bright pigments for applications, such as cosmetics, ink, and plastic paints for home appliances, other than the automotive body coating composed of a metallic base layer, there are flaky particles (glass flakes and mica) that are made of a material having a refractive index of 1.4 to 1.8, and that have an average thickness of 0.8 μm or more. However, if the thickness increases, a lot of coarse particles each having a particle size over 62 μm are included therein. Therefore, when using such a bright pigment for the automotive body coating composed of a metallic base layer, it is far from practical use because of the circulation property in which clogging of a filter occurs in application of the coating composition containing the bright pigment to the filter, and the coating finish in which proper orientation of the pigment in the coating film of the coating composition is prevented, thereby causing a part of the pigment to protrude or causing recognition that an excessively large pigment is a foreign object.
Even if adjusting the particle size as proposed in JP 2002-155240 A, it is difficult to achieve a bright pigment that can solve these problems completely, that is, to achieve a bright pigment having favorable properties in a balanced manner, in which an automotive body coating composed of a metallic base layer can be achieved having no mixture of various colors appearing in the particles, while a favorable circulation property and coating finish still are ensured.